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The Venus Entry Probe study is one of ESA's technology reference studies. It aims to identify; the technologies required to develop a low-cost, science-driven mission for in-situ exploration of the atmosphere of Venus, and the philosophy that can be adopted. The mission includes a science gathering spacecraft in an elliptical polar Venus orbit, a relay satellite in highly elliptical Venus orbit, and an atmospheric entry probe delivering a long duration aerobot which will drop several microprobes during its operational phase. The atmospheric entry sequence is initiated at 120 km altitude and an entry velocity of 9.8 kms-1. Once the velocity has reduced to 15 ms-1 the aerobot is deployed. This consists of a gondola and balloon and has a floating mass of 32 kg (which includes 8 kg of science instruments and microprobes). To avoid Venus’ crushing surface pressure and high temperature an equilibrium float altitude of around 55 km has been baselined. The aerobot will circumnavigate Venus several times over a 22-day period analysing the Venusian middle cloud layer. Science data will be returned at 2.5 kbps over the mission duration. At scientifically interesting locations 15 drop-sondes will be released. This paper focuses on the final mission design with particular emphasis on system level trade-offs including the balloon and pressurisation system, communications architecture, power system, design for mission lifetime in a hostile and acidic environment. It discusses the system design, design drivers and presents an overview of the innovative missionenabling and mission-enhancing technologies.

In order to meet the growing global requirement for affordable missions beyond Low Earth Orbit, two types of platform are under design at the Surrey Space Centre. The first platform is a derivative of Surrey’s UoSAT-12 minisatellite, launched in April 1999 and operating successfully in-orbit. The minisatellite has been modified to accommodate a propulsion system capable of delivering up to 1700 m/s delta-V, enabling it to support a wide range of very low cost missions to LaGrange points, Near-Earth Objects, and the Moon. A mission to the Moon - dubbed “MoonShine” - is proposed as the first demonstration of the modified minisatellite beyond LEO. The second platform - Surrey’s Interplanetary Platform - has been designed to support missions with delta-V requirements up to 3200 m/s, making it ideal for low cost missions to Mars and Venus, as well as Near Earth Objects (NEOs) and other interplanetary trajectories. Analysis has proved mission feasibility, identifying key challenges in both missions for developing cost-effective techniques for: spacecraft propulsion; navigation; autonomous operations; and a reliable safe mode strategy. To reduce mission risk, inherently failure resistant lunar and interplanetary trajectories are under study. In order to significantly reduce cost and increase reliability, both platforms can communicate with low-cost ground stations and exploit Surrey’s experience in autonomous operations. The lunar minisatellite can provide up to 70 kg payload margin in lunar orbit for a total mission cost US$16-25 M. The interplanetary platform can deliver 20 kg of scientific payload to Mars or Venus orbit for a mission cost US$25-50 M. Together, the platforms will enable regular flight of payloads to the Moon and interplanetary space at unprecedented low cost. This paper outlines key systems engineering issues for the proposed Lunar Minisatellite and Interplanetary Platform Missions, and describes the accommodation and performance offered to planetary payloads.

LunARSat, the Lunar Academic and Research Satellite, is a micro-spacecraft that will be sent into an orbit around the Moon to perform scientific investigations concerning the lunar environment and its characteristics. However, the prime objective of the LunARSat mission is to serve as an educational and outreach project. LunARSat is designed by young engineers, scientists, and students from around Europe, with support from numerous institutions and space industry. It shall be launched as an auxiliary payload on an Ariane 5 ASAP platform and will have a mass of 100 kg in GTO. LunARSat will orbit the Moon on a highly elliptical polar orbit with its perilune above the lunar south pole area. This orbital strategy yields the possibility to obtain images of the lunar south pole region with a resolution never achieved before. Further measurements shall provide further evidence regarding the existence of water ice in the lunar polar craters.

This paper presents the design of the University of Surrey's SNAP-1 nanosatellite which is planned for launch in 1999. The satellite is modular in design and is based entirely on "commercial-off-the-shelf' (COTS) technologies. The objective of the "SNAP" Programme is to provide a very low cost orbital test vehicle for micro-electro-mechanical systems (MEMS) and to provide practical education and training for engineers in the techniques and rigours a spacecraft design and construction.

State-of-the-art commercial microprocessors are attractive for use in cost effective space missions because, they are readily available, they are of high packaging density, cheap and capable of supporting extensive software. However, because they are not radiation hardened, they are susceptible to single event upset (SEU) caused by ionizing radiation. Being able to predict, in advance, the observable SEU induced error rate in a microprocessor is therefore essential. Using the 8051 processor as an example, a new method has being developed for this purpose and is presented here.

One way to achieve faster and cheaper small satellite missions is to make maximum use of off-the-shelf (OTS) technology. OTS subsystems are found in many small satellite missions, typically configured within a customized mission-specific space frame. Theoretically, costs and time-scales can be cut further by extending the OTS approach to the entire spacecraft, including mechanics, software and operations. This has been the objective of many "modular satellite" programs, including the Surrey Satellite Technology (SSTL) modular microsatellite bus. Since 1990, the basic SSTL bus has been applied to 11 missions carrying a wide variety of payloads into LEO. Inevitably, however, each mission has payload unique requirements that prevent the use of a purely OTS approach. Customers are willing to pay for some "alterations" to their OTS microsatellite, as long as the alterations don't cause unacceptable increases in cost, schedule, and/or performance risk. The initial difficult task for the prime mission contractor, payload customers, and spacecraft supplier is to arrive at a set of modifications which maximize the mission return while minimizing the impact on the cost, schedule, and performance baseline. This process requires a mutual understanding by all parties of the spacecraft's true capabilities as well as the payloads' minimum requirements. It also requires the payload customer to separate "desirements" from "requirements" and be willing to trade-off the former to prevent intolerable increases in cost and schedule. In many cases, with imagination from all parties, this customization process is successful and the resulting mission is still nearly OTS. This paper describes the USAF PICOSat mission, in which the SSTL OTS modular micro satellite was tailored to accommodate four unique science payloads from the U.S. Air Force Space Test Program (STP). This mission was enabled by funding from the Department of Defense Foreign Comparative Test Program. PICOSat, which will be built, integrated, tested and operated by SSTL in England, will carry the Polymer Battery Experiment (PBeX), the Ionospheric Occultation Experiment (lOX), the Coherent Electromagnetic Radio Tomography (CERTO) experiment, and the Optical Precision Platform Experiment (OPPEX), making it one of the most complex microsatellite missions executed to date. The PICOSat mission will run just 18 months between contract signing and launch readiness, including all tailoring of the platform hardware and software to accommodate the payloads-several of which existed prior to the commencement of the program. The methods used to accommodate these payloads and reach a compromise on cost, risk and experimental return are of interest to any group undertaking a multiple-payload small satellite mission based on off-the-shelf technology.

This paper describes observations of single-event memory upsets in the UoSAT-2 satellite Digital Communications Experiment. Two years of SEU observations for Harris 6564 memories are included, presented both as error rate statistics and as a map of satellite orbital location at the time of error occurrence. The results presented here are the preliminary observations in a long-term single-event upset study funded by ESA-ESTEC.